Go to the 'Extras' option at the 'Main' menu and select 'Promotional Unlocks' followed by 'Enter Code'. Then enter one of the following codes to activate the corresponding effect. Note: The 'Server-Driven Content' option in the 'Help & Options' menu may need to be enabled.

Viral Persona:
Enter X340F5IS979E7K3Q as a code and ignore the error message.

Promotional Card #1:
Enter GKSNDR as a code.

Promotional Card #2:
Enter DWNNDR as a code.

Promotional Card #3:
Enter FTHPTH as a code.

Promotional Card #4:
Enter TRCKSC as a code.

Promotional Card #5:
Enter PRSTTT as a code.

Foil Promotional Unlocks
On the player status page, click on the promotions page. From there at the bottom, hit the enter code button. Enter each of the following codes to unlock one card per deck, up to a total of 40 cards for each deck.

Promo Unlock 01
WMKFGC

Promo Unlock 02
KWPMZW

Promo Unlock 03
FNMDGP

Promo Unlock 04
MWTMJP

Promo Unlock 05
FXGJDW

Promo Unlock 06
GDZDJC

Promo Unlock 07
HTRNPW

Promo Unlock 08
NCTFJN

Promo Unlock 09
PCNKGR

Promo Unlock 10
GPCRSX

Steam Achievements
Acquire the Sliver Fossil: Defeat the "Sliver Hive" deck in campaign mode
Battlemaster: Win 75 games
Bloodless Triumph: Win a game while dealing no combat damage to a player
Burn Monster, Burn!: Lose the "Angry Mob" encounter
Chandra's Ally: Defeat Ramaz
Counter Crazy: Control a permanent with ten or more counters on it.
Death Dealer: Destroy and/or deal lethal damage to 300 creatures
Deck Eclectic: Win a game with each deck
Defeat Ramaz's Ally: Defeat the "Chant of Mul Daya" deck in campaign mode
Deflectomancer: Counter 25 spells
Field Marshal: Have 40 permanents on the battlefield
Flawless Victory: Win a game without losing any life
Heavy Hitter: Deal over 200 damage in the "Go Berserk" Challenge
Hivelord: Control seven or more Slivers with different names
In It to Win: Win 25 games
Land Lord: Control seventeen land of a single type
Lord of Foriys: Win a Two-Headed Giant game
Maestro of Sealed: Complete the Sealed campaign
Master of Magic: Unlock every deck
Masterful Strategist: Win a Multiplayer game
Recover the Scrying Shard: Defeat the "Enter the Dracomancer" deck in campaign mode
Sealed the Deal: Win a Sealed game
Secrets of the Dimir: Defeat the "Masks of the Dimir" deck in campaign mode
Skilled Tactician: Solve a Challenge
Slaughtermaster: Deal a total of 5000 damage
Sparer of Pawns: Win a game without destroying or dealing lethal damage to a creature
Spell Delver: Unlock 50 cards
Spellbook Complete: Fully unlock one deck
Super Sleuth: Solve every Challenge
Worthy Adversary: Defeat the "Avacyn's Glory" deck in campaign mode